This invention relates to an apparatus for cutting glass, more particularly, to the scoring of glass sheets preparatory to severing them into small rectangles or squares.
The type of glass cutting to which this invention is directed involved making a physical discontinuity, or score, on the surface of a sheet of glass or near the surface or both, followed by the application of a bending moment about the score line to snap the glass along the score line. The present invention is directed to an improvement in the means for placing the scores on a sheet of glass in the particular case of a relatively large sheet being subdivided into a large number of small pieces.
The prior art has advanced from the time-consuming practice of manually making each score individually to the use of ganged sets of scoring tools which simultaneously make a plurality of parallel scores in a single pass. These prior art devices are typically intended for such applications as subdividing large sheets of glass into a plurality of window panes, microscope slides, or blanks which are subjected to subsequent cutting operations and the like. Such applications generally have relatively liberal tolerance requirements, and therefore the scoring means used do not provide for the highly accurate spacing now required for certain specialized applications. One area in which a need for greater accuracy is required is in the process where a large number of discrete, electrically conductive patterns are coated onto a sheet of glass, and the sheet is subsequently subdivided into small rectangles with a pattern accurately located on each rectangle. Typical tolerance requirements for the cut products of this type are sometimes as small as .+-. 0.002 inch (.+-. 0.050 millimeters).
In many prior art glass multi-cutters, each scoring head is individually clamped or bolted in place, and the spacing between each scoring head is established manually. The following U.S. Patents show typical arrangements:
U.S. Pat. No. 2,377,096. . . . Owen
U.S. Pat. No. 3,286,893. . . . Zellers
U.S. Pat. No. 3,290,973. . . . Oakes et al.
U.S. Pat. No. 3,537,344. . . . Walsall et al.
U.S. Pat. No. 3,716,176. . . . Yamada et al.
U.s. pat. No. 3,626,795 to White shows a multi-cutter having spacer rings between each scoring head, and U.S. Pat. No. 3,151,794 to Brand discloses an arrangement wherein the spacing between a plurality of scoring heads is determined by adjustable bars. None of these prior art arrangements is particularly suited for eliminating the several sources of imprecision in the spacing of the score lines that are produced.
Major improvements in accurately locating a plurality of score lines are disclosed in U.S. Pat. Nos. 3,859,878 and 3,880,029, both to Bonaddio et al. There, the improvement is largely attributable to the use of a single, precision-made, interchangeable shaft guide for each scoring pattern. In order to reduce tolerances even further, it would be desirable to eliminate the clearance that is required between each scoring tool shaft and its shaft guide as well as the clearance that is necessary for a scoring wheel holer to pivot at the end of each shaft. it would further improve accuracy if the wobble of a scoring wheel within a slotted wheel holder could be reduced.